In a substrate processing apparatus, a substrate undergoing processing for semiconductor device production, such as a wafer, is carried into a processing chamber via a transfer means such as a transfer arm and a specific type of processing, e.g., etching or film formation, is executed on the wafer having been carried into the processing chamber. As increasingly fine circuit patterns have come to be formed through highly advanced micro-processing technologies in recent years, it has become necessary to position the wafer undergoing processing or inspection with a high level of positioning accuracy in correspondence to the nano-order device design specifications (e.g., circuit line width of 65 nm).
The wafer is usually positioned by, for instance, disposing a light emitting unit and a light receiving unit of a light-transmitting sensor so as to allow them to operate across the wafer edge, through which light radiated toward the wafer edge is transmitted and received as the wafer is rotated, obtaining data indicating the wafer edge shape based upon a change in the quantity of the transmitted light and detecting the direction and extent of misalignment of the wafer center relative to a specific position based upon the data thus obtained. The wafer center can be positioned based upon the detection results.
A notch mark, such as an indented notch or a linear notch, often referred to as an orientation flat, is formed at part of the edge of the wafer. As light is radiated onto the edge area of the rotating wafer, as described above, a relatively significant change occurs in the quantity of light transmitted over the notch mark. Accordingly, the presence of the notch mark is reflected in the wafer edge shape data, enabling accurate detection of the notch mark position. As a result, the wafer can be positioned along the circumferential direction based upon the circumferential shape of the wafer.
The wafer, having been accurately centered and positioned along the circumferential direction as described above, is then transferred to take a specific position inside the processing chamber with a high level of accuracy via a transfer means in the state in which its angle assumed along the circumferential direction has been adjusted.
Various technologies have been proposed to date in the area of wafer positioning. For instance, Japanese Laid Open Patent Publication No. H06-045226 (patent reference literature 1) discloses a positioning device that includes at least three linear sensors engaged in operation to set a wafer at a specific position and orient it in a specific direction accurately and quickly. Japanese Laid Open Patent Publication No. 2006-019388 (patent reference literature 2) discloses a technology that enables wafer positioning even when a wafer edge over which a notch is formed cannot be detected.
Wafers used in semiconductor device production include those constituted of sapphire glass, quartz glass and the like with superior light transmission characteristics and electrical insulation characteristics (hereafter referred to as “glass wafers”), as well as wafers constituted of a single-crystal silicon (hereafter referred to as “silicon wafers”). The linear advance of light perpendicular to the surface of such a glass wafer may be disallowed by beveling its entire edge, so as to enable detection of the beveled edge with a light transmitting sensor. Based upon the results of the edge detection, the glass wafer can be positioned accurately.
As disclosed in Japanese Laid Open Patent Publication No. H07-326665 (patent reference literature 3), we have seen the advent of two-layer composite wafers formed by layering the glass wafer and the silicon wafer described above one on top of the other. In addition, Japanese Laid Open Patent Publication No. H10-199809 (patent reference literature 4) above discloses a method for forming an amorphous silicon film over the surface of a glass substrate.
A composite wafer normally adopts a structure achieved by superposing a transparent wafer (transparent layer) with a high level of light transmissivity such as a glass wafer and a nontransparent wafer (nontransparent layer) such as a silicon wafer with low light transmissivity allowing hardly any light to be transmitted through, which assumes smaller external dimensions than the transparent wafer, one on top of the other with the entire edge of the transparent wafer extending beyond the edge of the nontransparent wafer.
The edge of the transparent wafer, equivalent to the outermost periphery of this composite wafer, will normally be beveled over the entire periphery. Accordingly, in edge shape data obtained by using a light transmitting sensor while rotating the composite wafer along the peripheral direction, theoretically, the edge of the transparent wafer should be detected as the edge of the composite wafer, since light does not advance linearly at the outermost edge of the transparent wafer.
However, depending upon the rotational angle, the edge of the transparent wafer is not always detected, due to, for instance, irregular reflection. If the edge of the transparent wafer is not detected, edge detection is executed inward and, as a result, the edge of the nontransparent wafer located further inward relative to the edge of the transparent wafer is detected as the edge of the composite wafer. In other words, there is a problem to be addressed in that depending upon the rotational angle, the edge of the transparent wafer or the edge of the nontransparent wafer may be detected as the edge of a composite wafer such as that described above and since valid edge shape data representing the edge of the composite wafer cannot be obtained, the wafer cannot be positioned accurately.
In particular, in the case of a composite wafer with a notch mark formed only at the edge of the nontransparent wafer, the notch mark cannot be detected if the edge of the transparent wafer is detected as the edge of the composite wafer, leading to a concern that the composite wafer cannot be positioned at all based upon the notch mark.